Certain textile-treatment operations, such as dyeing, leave the textile web being treated in a bunched-up and twisted together condition. Obviously marketing or further treating the web requires it to be smoothed out and flattened, so that some sort of automatic device must normally be provided which can draw the cloth out of a bin or other such container and flatten it out while eliminating the twist in it. Such an apparatus normally draws the cloth along a treatment path past a twist-sensing location. A spreader and flattener is provided upstream of the sensing location and a detwisting device is provided downstream of this location. In accordance with the twist sensed at the location the detwister twists the fabric in the opposite direction so as to eliminate its twist so that the following flattener and smoother can operate effectively on the cloth.
In German published patent application No. 2,315,892 (whose equivalent is U.S. Pat. No. 3,813,862 of June 4, 1974) the strand or web is passed over a fixed roller rotatable about a horizontal axis. The sensing location is immediately downstream of this roller and the detwisting device is upstream of this roller. At the sensing location the strand is pressed by means of a pressure plate into a slitted guide channel in whose slot a brush-type sensor roller engages from outside. This sensor roller is driven in a direction opposite the transport direction of the strand and is longitudinally displaceable along its drive shaft. Thus the bristles of this sensor roller engage the surface of the web, and will be urged to one side or the other in accordance with any twist in the web. End switches acted on by this sensor roller serve to operate the detwisting device to eliminate the twist upstream of the deflecting roller.
Such a system requires considerable tension in the strand for it to function, and requires that the pressure plate be urged with considerable force against the strand. Thus a delicate textile can easily be damaged by this system. Furthermore the detwister frequently adds twist to the textile web, in particular as such a web is normally most severely twisted at its free end, so that in overcoming this twist the detwister normally imparts a twist to the section upstream so that the entire web will be given this twist as it passes along the section.
In U.S. Pat. No. 3,693,336 such an apparatus is shown wherein the rope-like bundle formed by the cloth is passed through a rotatable tube guide whose entrance end is fitted with a plurality of smoothly curved protuberances which extend radially inwardly so as to contact the rope-like bundle tightly. Such an arrangement acts as a detwister, but requires that the textile be engaged with considerable force so as to detwist it. Furthermore, much as in the above-described German patent publication, the detwisting operation itself may add undesirable twist to the upstream portion of the strand.
From U.S. Pat. No. 2,759,324 an arrangement is known wherein the twisted strand is pressed flat between sensing rollers which extend perpendicular to the transport direction of the strand and which are laterally slidable on their respective axles. The extend of slide of the sensing rollers controls the rotary drive for the detwisting apparatus. Once again this apparatus relies on subjecting the arrangement at the sensing device to considerable mechanical manipulation so that a delicate cloth may be damaged. Furthermore, in order to draw the strand or web through these pinch rollers it is necessary to pull the strand or web with considerable force, once again risking damage to the web.
In German published application No. 2,216,753 it is known to form a so-called hot trail on the twisted strand. This trail is sensed and in turn operates the detwisting device. Such an arrangement is extremely complex and cannot be applied to certain types of textiles.